In existing wireless communications technologies, OFDMA (orthogonal frequency division multiplexing access), as a mature downlink multiplexing access technology, is widely applied to communication systems, such as LTE/LTE-A. One feature of the technology is that: one RB (resource block) may be formed by multiple REs (resource elements), and each RE forming one RB may bear different information, for example:
As shown in FIG. 1a, when downlink data is transmitted on a PDCCH, REs in one RB may be assigned like this: various reference signals such as information in the PDCCH channel, a cell-level reference signal (CRS), a user-level reference signal, and a channel state information reference signal (CSI-RS) may be mapped to the REs of black parts in the RB shown in FIG. 1a. 
The REs of white parts in the RB shown in FIG. 1a bear information of a control channel like a PDSCH or an ePDCCH, for example, control information of DCI. Further, the control information transmitted on the ePDCCH is mapped to a series of RBs by using an eREG as a basic resource unit, but the information processed by a device such as a base station in the wireless communication system is presented by an eCCE. One eCCE is formed by multiple eREGs, and the multiple eREGs forming one eCCE are from multiple RBs in the series of RBs. For example:
In the RB shown in FIG. 1b, non-marked parts are the REs corresponding to the configured eREGs in the RB. It should be noted that numbers in the figure are numbers of the eREGs in an actual application, for example: an eREG 0 is formed by REs numbered 0 in the non-marked parts. The number of REs corresponding to eREGs 0-7 is respectively 16, 12, 15, 14, 12, 13, 12, and 14, that is, a size of each eREG is different. The size of the maximal eREG is 16 REs, and the size of the minimal eREG is 12 REs, where a difference is four REs. Further, multiple corresponding eREGs in multiple RBs form one eCCE. For example, in the prior art, eREG 0 in RB0 and eREG 0 in RB1 form one eCCE together; and eREG 1 in RB 0 and eREG 1 in RB1 form another eCCE. Similarly, multiple eCCEs may be finally obtained, for example, eight eCCEs numbered from eCCE a0 to eCCE a7.
However, the inventor finds that the prior art has the following problem:
If the eREGs forming a same eCCE are from two adjacent RBs, for example, RB0 and RB1, it may be caused that channel frequency diversity of the two eREGs forming the eCCE is poor during a transmission process, while poor frequency diversity causes information being processed by a terminal device to get lost, for example, a bit error rate or block error rate of control information sent by a base station and received by the terminal device is relatively high, thereby lowering performance of the communication system. For example, in a case that information loss occurs, the base station needs to resend the information, thereby further the performance of the communication system.